Organic light-emitting devices with in situ postgrowth annealed organic layers -: art. no. 063505

A comparative study of in situ postgrowth annealing of organic layers before metal cathode was conducted on tris-(8-hydroxyqunoline) aluminum (Alq(3))-based organic light-emitting devices (OLEDs). The devices were fabricated in the same run with a standard device without annealing for comparison, with an identical structure of indium tin oxide (ITO)/copper phthalocyanine (CuPc) (10 nm)/N,N'-di(naphthalene-1-yl)-N,N'-diphenyl-benzidine (NPB) (90 nm)/Alq(3) (90 nm)/Mg:Ag (200 nm)/Ag (20 nm). The annealing temperature used was 60, 80, and 100 degrees C, respectively. It was found that, in situ postgrowth annealing improves the device performance, and annealing near the glass transition temperature of NPB (99.7 degrees C), improves device performance drastically. Power efficiency and current efficiency increase significantly with the annealing temperature, except the current efficiency for device annealed at 100 degrees C is slightly lower than that of the standard device. The voltage and current density for 100 cd/m(2) luminance are 5.6 V and 4.4 mA/cm(2), respectively, for the device annealed at 100 degrees C, in comparison to 9.2 V and 4.3 mA/cm(2), respectively, for the standard device, the power efficiency is much improved by more than 40%. The in situ postgrowth annealed organic layers were characterized by photoluminescence and Raman spectroscopy. (c) 2005 American Institute of Physics.